The present invention relates to an automotive seat safety mechanism that is installed in an automotive seat and functions when a collision occurs.
In the prior art, in addition to the employment of a three-point safety belt, which restrains a passenger to an automotive seat, mechanisms for increasing the strength of the seat itself has been proposed to resist impacts. For example, Japanese Laid-Open Patent Publication No. 2001-213211 describes a mechanism in which a webbing is arranged between a seat back and the roof of a vehicle. When an impact load is applied to the seat back, the webbing, which is drawn into a retractor, is locked. This securely supports the head rest and protects the head of the passenger.
In such case, the webbing functions as a reinforcing member and supports the seat back from the roof. However, such webbing has a shortcoming in that it reduces the interior space in the rear of the vehicle and interferes a passenger who gets into or out of the rear of the vehicle. Accordingly, it is preferable that the webbing be extended vertically upward from the seat back, as described in Japanese Laid-Open Patent Publication No. 2001-213211, so that the webbing does not extend in a rearward direction from the seat back.
However, since the seat back is normally inclined toward the rear when a passenger is sitting on the seat, the webbing described in the publication may not be able to efficiently support the seat back when an impact is applied to the seat back.
Referring to FIGS. 18 and 19, a webbing 100 functions to reinforce an automotive seat 101. When an impact is applied to the rear of the vehicle (hereinafter, referred to as rear crash), a rotational moment acting to pivot the seat back 101 toward the rear (rearward pivoting) about basal portion O is applied to the seat back 101. In such case, the rotational moment locks the webbing 100. Thus, the locked webbing 100 supports the seat back 101 when the seat back 101 starts rearward pivoting. In other words, the webbing 100 directly counters the rotational moment, which is produced by the impact.
When an impact is applied to the front of the vehicle (hereinafter, referred to as front crash), a rotational moment acting to pivot the seat back 101 toward the front (forward pivoting) about basal portion O is applied to the seat back 101. However, unlike during a rear crash, the forward pivoting of the seat back 101 first loosens the webbing 100. Thus, the webbing 100 is not immediately locked. Theoretically, the webbing 100 is not locked until a force that pulls the webbing 100 is produced when the seat back 101 exceeds line P, which connects the basal portion Q of the webbing 100 and the pivoting center of the seat back 101, as shown in FIG. 19.
Therefore, during a front crash, the webbing 100 may not sufficiently absorb the impact and restrain the seat back 101.
Further, the impact load applied to the seat back 101 may be stronger during a front crash than during a rear crash. For example, a passenger sitting in the rear seat may be thrown against the seat back 101 during a front crash. Additionally, when a rear passenger air bag is installed in the seat back 101, the impact (reaction) resulting from the activation of the air bag may produce a rotational moment that results in forward pivoting of the seat back 101.
Accordingly, there is a demand for a mechanism that functions to sufficiently support a seat back during a front crash.